The automotive industry has worked for decades to increase the fuel efficiency of vehicles by, for example, replacing a significant amount of the steel once used to manufacture vehicles by lighter parts made of polymeric resins. At the same time, the industry has moved toward recycling components of vehicles in order to reduce consumption of natural resources. Modern thermoplastics have improved physical properties, such as good tensile strength for a structural component or good impact strength for a bumper, and can be recycled.
While satisfactory functional properties can be achieved with different known thermoplastic materials, there remains a need for thermoplastic materials having an improved appearance. There is a particular need in the automotive market for thermoplastic materials that can be colored to match the appearance of the painted exterior of the vehicle, while maintaining physical properties suited to the particular application. Matching the appearance of the paint has been difficult in view of the extensive automotive color palette, which includes, for example, metallics and other special-effects coatings. In addition, the finish of a vehicle is expected to be of the highest quality in smoothness, glossiness, and depth of image.
In the past, exterior automotive plastic parts have usually been either painted or laminated with a film in order to match the coating on the body of the vehicle. Painting of the plastic parts is problematic for a number of reasons. First, the parts are irregularly shaped, and it is often difficult to apply a smooth film of uniform thickness to all required surfaces. Second, one of the largest sources of regulated emissions in an automotive assembly plant is the paint shop, where the various layers of the finishing materials are applied. In addition, the paint shop is one of the most expensive areas when an automotive plant is constructed due to the need to apply a number of separate layers, with two or more required ovens to cure the various layers, and the emissions control equipment necessary to reduce emissions in the large volumes of waste air that result from spray painting operations. Thus, having a separate painting process requires more manufacturing floor space for the coating line and ovens. Third, the painting process adds to the cost and time of producing the elastomeric parts and articles. Fourth, the paint layer on the article can experience unsightly peeling and other delamination problems while in use, as well as low-temperature cracking due to poorer flexibility of the coating in comparison to the elastomeric article. Finally, it is often difficult to develop good properties in the applied coating because of the limited temperatures available for thermosetting the coating due to the need to avoid deforming the piece.
A number of improved plastics for exterior parts or methods for eliminating the need to paint the exterior parts of vehicles have been proposed. Certain exterior parts may be formed from colored polyvinyl chloride materials. Only certain parts may be made from polyvinyl chloride because of the properties that can be achieved with this material. One limited edition sports car, the DeLorean, was produced with an unpainted metal skin. Using natural metal exterior, however, limits the colors that can be made available.
Duvdevani et al., U.S. Pat. No. 4,268,552, disclose front and rear fascia formed by injection molding an elastomeric-rich inner core of a blend of a neutralized sulfonated elastomer and a polyolefin, and an outer shell or skin of a polyolefin. The Duvdevani reference teaches that the fascia must be painted in order to achieve a desirable finish.
Papendick et al., U.S. Pat. No. 5,037,680, disclose an exterior automotive vehicle component of thermoplastic polyolefin that is pigmented to a color suitable for the vehicle exterior. The component must then be provided with an outer layer of a clear coating in order to achieve the desired gloss, luster, mar resistance, and durability. Moreover, in the case of metallic colors, which dominate the automotive finishing market, the flake pigments must be included in the clear coating layer and cannot be used in the polyolefin composition. Such separation of flake pigments and color pigments may make it difficult to match the look of a painted exterior body, where both flake and color pigments are mixed in the same layer of paint and overcoated with a clear layer of paint. In addition, the clear coated components of the Papendick reference are susceptible to the same problems of delamination, color shifts and appearance changes accompanying delamination or scratching as accompany parts that are painted in the traditional way.
Rohrbacher, U.S. Pat. No. 5,055,346, discloses a process of forming laminate of acrylic thermoplastic paint layers on a flexible thermoformable polymeric material. The laminate and a rigid synthetic resinous substrate are separated formed to desired shapes. Finally, the formed laminate is adhered to the rigid substrate.
Kobayashi et al., U.S. Pat. No. 5,574,087, disclose a molded protective strip molded by gas injection molding from a mixture of one of isotactic propylene homopolymer or propylene bock copolymer with ethylene-propylene copolymer. Colorable compositions are not disclosed.
Terada et al., U.S. Pat. No. 5,574,087, disclose forming large exterior automotive exterior parts from a blend of polypropylene, a vanadium compound-catalyzed ethylene-propylene copolymer rubber, a titanium compound-catalyzed ethylene-propylene copolymer rubber, and a polyethylene. The formed parts must be painted.
Gubitz et al., U.S. Pat. No. 5,208,081, disclose a molding composition comprising isotactic polypropylene or propylene and ethylene copolymers, combined with a rubber-like, polypropylene-compatible copolymer.
Finally, Chrysler Corporation has recently publicly displayed a concept car, the Plymouth Pronto, having body panels made of acrylonitrile-styrene-acrylate thermoplastic with molded-in color. The car is a vanilla straight-shade (i.e., non-metallic). Unlike painted vehicles, for which the finish is smooth and glossy, the concept car has a textured, matte finish.
Thus, it would be desirable to have an article that can be used on the exterior of an automotive vehicle and later removed and recycled for further use. It would further be desirable to provide a material that can be formed processed into colored articles, wherein the color of the material gives the article a pleasing appearance, and preferably may color match an adjacent surface without painting.
We have discovered that an elastomer modified polyolefinic material having high transparency and/or clarity when unpigmented, as measured by light transmission and/or haze, can be pigmented with special effect pigment to produce articles and parts in desired colors with paint quality appearance. In particular, in one embodiment the inventive blend compositions can be pigmented and formed into automotive parts that match the exterior colors of automotive vehicle bodies. The blend compositions may be formulated to provide desirable physical properties, such as excellent flexibility, measured as ease of distortion under an applied load, suitable for bumper fascia.
In a second preferred embodiment, the elastomer modified polyolefinic material is formulated to give the strength and toughness necessary for an automotive body side cladding.